Cycles: how to get glass reflexion on precious stones
Lighting glossy surfaces is always about dealing with whatever is reflected on them.
I think your setup is quite nice, but in my opinion the reflections on the glass could be brighter. I would add more contrast to the surrounding dome's texture.
On the dome you are using for lighting you might want to change the texture to the color input socket and have the intensity be a value you can control:

In this example I'm using a dome with a voronoi texture to create a somehow random pattern for the light. The curves let you control the contrast. The whole idea is to get an interesting a pattern to reflect on the glossy surfaces.